#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef double db;

#define in read()
#define pii pair<int,int>
#define fi first
#define se second
#define FILE(x) freopen(x".in","r",stdin);\
	freopen(x".out","w",stdout);
#define pb push_back

int read(){
	int x = 0,sgn = 1;char ch = getchar();
	for(;!isdigit(ch);ch = getchar()) if(ch == '-') sgn = -1;
	for(;isdigit(ch);ch = getchar()) x = (x<<1)+(x<<3)+(ch^48);
	return x*sgn;
}

const int N = 2010;
const int inf = 0x3f3f3f3f;

int h[N],dis[N],incf[N],cnt = 1,cost,maxflow,pre[N],n,m,t[10][65],S,T;
bool vis[N];
struct edge{int v,w,c,nxt;}e[N<<6];
void link(int x,int y,int w,int c){e[++cnt] = (edge){y,w,c,h[x]};h[x] = cnt;e[++cnt] = (edge){x,0,-c,h[y]};h[y] = cnt;}

bool spfa(){
	memset(vis,0,sizeof vis); memset(dis,0x3f,sizeof dis); dis[S] = 0; vis[S] = 1; queue<int> q; q.push(S); incf[S] = inf;
	while(q.size()){
		int x = q.front(); q.pop();
		for(int i = h[x],y;i;i = e[i].nxt){
			if(dis[y = e[i].v] > dis[x] + e[i].c && e[i].w){
				dis[y] = dis[x] + e[i].c; pre[y] = i; incf[y] = min(incf[x],e[i].w); if(!vis[y]) vis[y] = 1,q.push(y);
			}
		}vis[x] = 0;
	}return dis[T] < inf;
}

void update(int x = T){
	while(x ^ S) {int i = pre[x]; e[i].w -= incf[T]; e[i ^ 1].w += incf[T]; x = e[i ^ 1].v;}
	cost += incf[T] * dis[T]; maxflow += incf[T];
}

int id(int x,int y){return (x - 1) * n + y;}

int main (){
#ifndef ONLINE_JUDGE
	freopen("1.in","r",stdin);
#endif
	m = in,n = in;
	for(int i = 1;i <= n;i++)
		for(int j = 1;j <= m;j++) t[j][i] = in;
	for(int j = 1;j <= m;j++)
		for(int i = 1;i <= n;i++){
			for(int k = 1;k <= n;k++){
				link(id(j,i) + n,k,1,t[j][k] * i);
			}
		}
	S = 0; for(int j = 1;j <= m;j++) for(int i = 1;i <= n;i++) link(S,id(j,i) + n,1,0);
	T = m * n + n + 1; for(int i = 1;i <= n;i++) link(i,T,1,0);
	while(spfa()) update();
	printf("%.2lf\n",1. * cost / n);
	return 0;
}

